From 6a50c9b512f7734bc356f4bd47885a6f7c98491a Mon Sep 17 00:00:00 2001 From: Ran Xiaokai Date: Fri, 7 Jun 2024 17:40:48 +0800 Subject: mm: huge_memory: fix misused mapping_large_folio_support() for anon folios When I did a large folios split test, a WARNING "[ 5059.122759][ T166] Cannot split file folio to non-0 order" was triggered. But the test cases are only for anonmous folios. while mapping_large_folio_support() is only reasonable for page cache folios. In split_huge_page_to_list_to_order(), the folio passed to mapping_large_folio_support() maybe anonmous folio. The folio_test_anon() check is missing. So the split of the anonmous THP is failed. This is also the same for shmem_mapping(). We'd better add a check for both. But the shmem_mapping() in __split_huge_page() is not involved, as for anonmous folios, the end parameter is set to -1, so (head[i].index >= end) is always false. shmem_mapping() is not called. Also add a VM_WARN_ON_ONCE() in mapping_large_folio_support() for anon mapping, So we can detect the wrong use more easily. THP folios maybe exist in the pagecache even the file system doesn't support large folio, it is because when CONFIG_TRANSPARENT_HUGEPAGE is enabled, khugepaged will try to collapse read-only file-backed pages to THP. But the mapping does not actually support multi order large folios properly. Using /sys/kernel/debug/split_huge_pages to verify this, with this patch, large anon THP is successfully split and the warning is ceased. Link: https://lkml.kernel.org/r/202406071740485174hcFl7jRxncsHDtI-Pz-o@zte.com.cn Fixes: c010d47f107f ("mm: thp: split huge page to any lower order pages") Reviewed-by: Barry Song Reviewed-by: Zi Yan Acked-by: David Hildenbrand Signed-off-by: Ran Xiaokai Cc: Michal Hocko Cc: xu xin Cc: Yang Yang Cc: Signed-off-by: Andrew Morton --- include/linux/pagemap.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'include/linux') diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index ee633712bba0..59f1df0cde5a 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -381,6 +381,10 @@ static inline void mapping_set_large_folios(struct address_space *mapping) */ static inline bool mapping_large_folio_support(struct address_space *mapping) { + /* AS_LARGE_FOLIO_SUPPORT is only reasonable for pagecache folios */ + VM_WARN_ONCE((unsigned long)mapping & PAGE_MAPPING_ANON, + "Anonymous mapping always supports large folio"); + return IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && test_bit(AS_LARGE_FOLIO_SUPPORT, &mapping->flags); } -- cgit v1.2.3